@article {aja2014noise, title = {Noise estimation in parallel MRI: GRAPPA and SENSE}, journal = {Magnetic resonance imaging}, volume = {32}, number = {3}, year = {2014}, pages = {281{\textendash}290}, publisher = {Elsevier}, author = {Santiago Aja-Fern{\'a}ndez and Gonzalo Vegas-S{\'a}nchez-Ferrero and Antonio Trist{\'a}n-Vega} }